Henderson Lake drawdown planned to fight hydrilla takeover

To get an idea of what a nuisance the water weed hydrilla can be, consider its name is derived from Hydra, the mythological nine-headed creature that grew back two heads for every one that was cut off.

The monster invaded Henderson Lake in St. Martin Parish years ago — choking the popular waterway, crowding out native plants, fouling boat propellers.

Parish officials believe they now have a plan that, while not killing it off, can at least tame it.

“We have come to the realization that we are never going to get rid of all of it,” said St. Martin Parish President Guy Cormier.

He said the hope is to knock back the plant’s growth by lowering water levels about 2 feet every summer, enough to dry out the shallow areas in the roughly 5,000-acre lake and kill the hydrilla lurking there.

“Just doing that will expose about 75 percent of the hydrilla,” Cormier said.

The annual drawdown also could nurture a more natural ecosystem, restoring the old cycle of flooding and drying out at Henderson Lake and other areas of the Atchafalaya Basin before flood-control projects decades ago sectioned off the swamp with levees, said Mike Wood, director of inland fisheries for the state Department of Wildlife and Fisheries.

“We would certainly like to mimic the natural fluctuation the lake had when it was connected to the Atchafalaya (River),” he said.

Hydrilla is an invasive plant from Asia that found its way into the wild after being brought to the U.S. by way of Florida in the 1950s for use as an aquarium plant.

The weed had spread throughout Louisiana by the 1980s.

It’s a particular problem at Henderson Lake because hydrilla thrives in the expanses of shallow water there, Cormier said.

The state has tried herbicide, spending more than $1 million in recent years to fight hydrilla and water hyacinth, another invasive weed at Henderson Lake.

Wood said killing of the hyacinth can actually exacerbate the hydrilla problem, because hyacinth floats on the surface and removing it allows more light to reach the hydrilla, which grows from the bottom.

The plan calls for lowering the water level at the lake to kill off the bulk of the hydrilla, then releasing grass-eating carp into the lake to dine on the remains, Wood said.

Henderson Lake has been lowered in the past to kill off the weed, but the strategy has not been sustained for several years in a row because the lower water levels can leave boat launches used by recreational boaters and swamp tour operators high and dry.

“We were having problems getting the public to the deeper water,” Cormier said.

A dredging project last year cut new channels from popular boat launches, Cormier said, allowing access to deeper areas of the lake that are still usable even if the water drops by 2 feet.

“We will have access to the lake,” said Sherbin Collette, mayor of the town of Henderson on the edge of the lake and a commercial fisherman who said he’s on the water there almost every day.

Collette said the biggest advantage he sees in drawing down the lake to control invasive weeds is that it doesn’t cost anything because the only work involved is to open up a water control gate to let the water flow out.

“All we have to do is press a button,” he said. “Mother Nature takes care of it.”

The mayor said there will likely be some concerns about the planned drawdown.

“Once people see the proof of what we’re doing, they will be for it,” Collette said.

Cormier said it can actually improve fishing because fish congregate in a smaller area when water levels are low.

St. Martin Parish Government still needs federal approval for the proposed drawdown and has applied to the U.S. Army Corps of Engineers this month to secure a permit for the project.

The drawdown would begin this year if the Corps approves the permit, he said.